An eco-friendly vehicle includes a hybrid vehicle, a plug-in hybrid vehicle, an electric vehicle, a fuel battery vehicle and the like, and among them, the plug-in hybrid vehicle and the electric vehicle may be charged by a user using a household AC power source and equipped with an on-board battery charger (OBC).
The OBC mounted within the plug-in hybrid vehicle and the electric vehicle consists of an EMI filter for removing a noise from an AC power source, a PFC converter for controlling a power factor, and a DC-DC converter for controlling insulation and an output current.
An LLC converter, as a resonant-type PWM converter, hardwarely uses a switching method for enhancing efficiency. However, a conventional non-resonant-type PWM converter uses a method for controlling output voltage and current by adjusting a duty, while the LLC resonant-type PWM converter uses a method for controlling output voltage and current by adjusting a switching frequency. Efficiency of the LLC resonant-type PWM converter heavily depends on an operational range of the switching frequency, and it is very important for the switching frequency to locate a resonance frequency.
Conventionally, the DC link voltage (input voltage of LLC converter=output voltage of PFC converter) instruction was generated by sensing output voltage and output current of the LLC converter, and therefore no required DC link voltage was generated when a sensing error was occurred. To this end, the LLC converter did not operate at the resonance frequency, and therefore there was a problem to reduce efficiency of the OBC. Furthermore, conventionally, since the DC link voltage instruction was generated by a map extraction, there was needed the step of checking the switching frequency in all intervals of the output voltage and the output current, and therefore, inevitable problems of additional manpower and cost may exist.
Accordingly, there has been needed a solution that allows the switching frequency of the LLC converter to operates at the resonance frequency and solves these problems.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.